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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Don't emit Win64 pdata/xdata for "leaf" functions"
href="https://llvm.org/bugs/show_bug.cgi?id=30337">30337</a>
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<th>Summary</th>
<td>Don't emit Win64 pdata/xdata for "leaf" functions
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>hans@chromium.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Blocks</th>
<td>26299
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>From <a href="https://msdn.microsoft.com/en-us/library/ms235286.aspx">https://msdn.microsoft.com/en-us/library/ms235286.aspx</a>:
"Leaf functions are functions that do not change any non-volatile registers. ..
Leaf functions can be unwound simply by simulating a return, so pdata and xdata
are not required."
Not emitting these would be good for binary size.
Note that such functions can still tail-call others, so they're not really
leafs in the call-graph sense.
If we hook up a way to determine whether a function is a leaf in this sense, we
can also use it to do conditional tail-calls for Win64. Such calls would
generally confuse the unwinder, but in leaf functions they are fine.</pre>
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</p>
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